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Merged
merged 7 commits into from
Jul 26, 2018
Merged

Suggest to take and ignore args while closure args count mismatching #52647

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87f0c1f
Suggest to take and ignore args while closure args count mismatching
csmoe Jul 23, 2018
27c0d56
Mark the suggestion applicable
csmoe Jul 23, 2018
a71deb2
Fix ui test
csmoe Jul 24, 2018
9492176
Suggest in separate line
csmoe Jul 25, 2018
40c0339
Fix test
csmoe Jul 25, 2018
d5256b7
Update comment and do suggest
csmoe Jul 25, 2018
1d79588
Update ui test
csmoe Jul 25, 2018
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23 changes: 23 additions & 0 deletions src/librustc/traits/error_reporting.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1050,6 +1050,29 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
if let Some(found_span) = found_span {
err.span_label(found_span, format!("takes {}", found_str));

// Suggest to take and ignore the arguments with expected_args_length `_`s if
// found arguments is empty(Suppose the user just wants to ignore args in this case).
// like `|_, _|` for closure with 2 expected args.
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            // Suggest to take and ignore the arguments with expected_args_length `_`s if
            // found arguments is empty (assume the user just wants to ignore args in this case).
            // For example, if `expected_args_length` is 2, suggest `|_, _|`.

if found_args.is_empty() && is_closure {
let mut underscores = "_".repeat(expected_args.len())
.split("")
.filter(|s| !s.is_empty())
.collect::<Vec<_>>()
.join(", ");
err.span_suggestion_with_applicability(
found_span,
&format!("change the closure to take and ignore the expected argument{}",
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Nitpick: I feel that this would read better as "you can change the closure...". That way we don't imply to the user that this is what they must do, only something they can do.

if expected_args.len() < 2 {
""
} else {
"s"
}
),
format!("|{}|", underscores),
Applicability::MachineApplicable,
);
}

if let &[ArgKind::Tuple(_, ref fields)] = &found_args[..] {
if fields.len() == expected_args.len() {
let sugg = fields.iter()
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8 changes: 8 additions & 0 deletions src/test/ui/mismatched_types/closure-arg-count.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,10 @@ LL | [1, 2, 3].sort_by(|| panic!());
| ^^^^^^^ -- takes 0 arguments
| |
| expected closure that takes 2 arguments
help: change the closure to take and ignore the expected arguments
|
LL | [1, 2, 3].sort_by(|_, _| panic!());
| ^^^^^^

error[E0593]: closure is expected to take 2 arguments, but it takes 1 argument
--> $DIR/closure-arg-count.rs:17:15
Expand Down Expand Up @@ -51,6 +55,10 @@ note: required by `f`
|
LL | fn f<F: Fn<usize>>(_: F) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^
help: change the closure to take and ignore the expected argument
|
LL | f(|_| panic!());
| ^^^

error[E0593]: closure is expected to take a single 2-tuple as argument, but it takes 2 distinct arguments
--> $DIR/closure-arg-count.rs:26:53
Expand Down